The crucial hearing tomorrow before a federal judge in Southern California focuses on the battle between the tech giant and federal investigators who want help from Apple to unlock an iPhone linked to one of the shooters in the December terror attack in San Bernardino, California.

"It's a fight over the future of high-tech surveillance, the trust infrastructure undergirding the global software ecosystem, and how far technology companies and software developers can be conscripted as unwilling suppliers of hacking tools for governments," wrote Julian Sanchez, asurveillance law expert at the libertarian Cato Institute in Washington.

"It's also the public face of a conflict that will undoubtedly be continued in secret, and is likely already well underway."

Apple, backed by a broad coalition of technology giants like Google, Facebook and Yahoo, argues that the FBI is seeking a "back door" into all iPhones as part of the probe into the December 2 massacre that left 14 people dead.

It also contends that the government is overstepping legal bounds by using a statute called the All Writs Act, which dates back to 1789, in order to force Apple to hack into the iPhone in question.

The company says that in deciding the case, the court must take into account the "broader context" which touches on the larger debate over data privacy.

The government has fired back, saying that Apple was not above the law and that its request for technical assistance concerns a single case - the Apple iPhone 5C, which was shooter Syed Farook's work phone from the San Bernardino health department.